Antenna



May l0, 1949.l

R. E; LAPP ANTENNA Fild sept. 14, v1945 FIG. I

FIG. 5

INVENTOR. ROGER .cLAP'P A 7' TORNEY Patented May 10, 1949 ANTENNA Roger E. Clapp,

Cambridge, Mass., assignor, by

mesne assignments, to the United lStates of America as represented by the Secretary of War Y Application September 14, 1945, Serial No. 616,370

(Ol. Z50-33.65)

3 Claims.

This invention relates to antennas for radi-o communication systems and particularly to antennas having means for obtaining an energy distribution pattern closely approximating the relation of csc26 in elevation, where 0 is the radiation angle measured from the axis of the radiating means or of the undis'torted or symmetrical radiation pattern normally produced by the radieting means.

In certain radio object locating systems, it is desirable that the energy distribution in a vertical plane be such that the variation of energy density versus the radiation angle approximates a cosecant-squared function. This distribution provides generally uniform echo strength for targets disposed at substantially equal elevation with respect to the antenna regardless of whether the target is close in or distant.

1t is the principal object of the present invention to provide an antenna adapted to produce a radiation pattern of csc20 configuration which has a uniform ground return characteristic over a reasonable range of altitudes.

It is another object of the invention to provide a linear `array antenna with reilector means for desired shaping .the radi-ation pattern.

Other novel features and advantages of the in? vention will become apparent from the following description with reference to the accompanying drawings in which:

Fig. 1 is a partly diagrammatic side elevation of .a linear array antenna illustrating one embodiment of the present invention and the radiation pattern produced thereby;

Fig. 2 is a side elevation similar to Fig. 1 showing a mod ication of the invention; `and Fig. 3 is a perspective view of a linear array antenna showing more clearly the reecting means according to the modification of Fig. 2.

Referring now to Fig. 1, I designates a longitudinal wave guide having broad walls I I and I2 and narrow walls I3 and I4. Along the length of broad wall I I and substantially midway of the width thereof there are, physically mounted, a plurality of spaced aligned dipoles I5 of conventional design having means for coupling to the energy propagated in wave guide I0. As so far described, this generally constitutes a linear array scanning antenna such as is disclosed in the co-pending application Serial No. 542,287, iiled June 27, 1944, in the name lof Luis W. Alvarez. While the lpresent invention is principally direc'ted to a linear array antenna such as disclosed in the aforesaid co-pending application, it will be 2 understood that the invention is not limited thereto but may apply to any similar antenna.

On opposite sides of (or as shown above and below) the row of dipoles I5, there'are mounted reflector plates I5 and Il. Reflector plate I'I is preferably a plane substantially rectangular sheet of electrically conductive material having one edge secured substantially along the length of wave guide I@ and at an acute angle to a plane through the dipoles I5 and perpendicular to broad wall I I. Reflector plate |46 is also a sheet of electrically conductive material having one edge secured along the length of wave guide It with its major portion also disposed at an acute angle to broad wall II. The combination of plates IB and Il as seen in side elevation in Fig, 1 give the appearance of a horn flared outwardly away from wave guide III and the effect is similar to that of a flared horn with respect to the eiiciency of radiation and impedance matching.

The outer edge portions of plate II has one or more, and preferably three, sharp bends or in other words is bent along its length one or more, and preferably three times in alternate directions, t-o produce the conguration shown in side View in Fig. 1, the bends appearing as substantially parallel lines in a top plan View. The free edge portion I8 :of plate IIB is preferably bent downwardly toward plate I'I so that the side view configuration of the bent portion is substantially Z-shaped. Radiation from dipoles I5 impinges upon the angularly related surfaces of upper plate I6 and is generally reflected downwardly ,while plate I'I acts to reect the energy ahead of the antenna and also acts to cut off sharply the lower portion of the radiation pattern. By suitable design of the bent portion or portions of plate I'G and of the angular relation of plates I6 and II, any desired radiation pattern may be produced including a pattern of c8020 configuration as indicated by dotted lines in Fig. 1.

The radiation pattern obtained from the plates in Fig. 1 was found to be particularly satisfactory when the antenna was enclosed within a rounded leading edge type vane I9 as indicated in the dash lines of Fig. 1. The phasing of the reflection from plates |16 and I'I in combination with the reections from the interior surface of the vane I9 was such that the radiation pattern had small secondary lobes and holes in the main lobe were sufficiently lled out t-o give uniform ground return through the scanning range. However, for .a more streamlined vane I9 such as indicated in broken lines in Fig. 2, it was found that with the particular design of the reflector plates t5 and Il as shown in Fig. 1 the streamlined vane I9 caused some out-of-phase reflections. To overcome these disadvantages, the modification as shown in Figs, 2 and 3 was developed.

In Figs. 2 and 3, the parts similar to those described with reference to Fig. l are shown in prime numbers. rPlates I6 and I7' are shaped and disposed in a similar manner as that described in Fig. 1 except that the rear edges of the plates are disposed forwardly of the broad wall Il'. Thus, the rear edges of plates i6 and I1 are connected to and along the forward edges of parallel plate members 20 and 2l. The parallel plate members 20 and 2l are disposed'substantially perpendicular to broad wall l i', above and below the row of dipoles l5 and may be secured directly to the broad wall l I. Preferably, parallel plate portions 20 and 2l, are disposed forwardly of the wave guide l so that the rear edges vof plates 20 and 2l are substantially the same distance from wall H as the dipoles l. Thus, reflector plates i6 `and Il', including the parallel plate portions and 2l may be mounted `0n wave guide l0 by means of spaced supporting members 22 secured to broad wall il in any suitable manner (Fig. 3). I f desired, flanges 23 and 24 are provided to insure greater strength,

such ilanges being disposed along the rear edges of parallel plate portions 20 and 2i and substantially parallel with wall Il'.

The eect of arranging the reflector plates I6 and H' with the parallel plate portions 2G and 2| forwardly of the wave guide l0 as herein described is that `the radiation from dipoles 'I5' is channeled by the parallel plate members .-20 and 2l, the phasing of the radiation is made more uniform and is effective to oset the outof-phase reflections which would be caused by the vane I9 itself.

Whiletherehas been described what is at present considered the preferred embodiments of the invention, 'it will be obvious to those skilled in the art that Various changes and modifications may -be lmade therein without departing from the invention.

What is claimed is:

1. In a linear array antenna having a longitudinal waveguide, means for propagating energy within said wave guide, a plurality of dipoles aligned along one of the walls of said wave guide, means for shaping the radiation pattern `produced by said dipo1es,said means comprising two reflector plates one disposed above and the other below said aligned dipoles, said reflector plates being arranged at an angle to said wall of said wave guide and flared outwardly away from each other, one of said reflector plates having a plurality of bends in alternate directions in the end portion remote from said wall to form a plurality of angularly disposed reilecting surfaces, said'bends being substantially parallel lines along the length of said reflector plate, said angularly disposed reflecting surfaces being effective to direct energy radiated from said dipoles in any desired radiation pattern.

2. An antenna as claimed in claim 1 in which the reflector plates are connected along the rear edge to parallel plate portions disposed perpendicularly to the'wave guide, and inr which spaced supporting membersy connect said parallel plate portions and said reflector plates to said wave guide, whereby said reflector plates and said parallel plate portions are positioned forwardly of said waveguide and of said dipoles.

3. In a linear array antenna having a longitudinal wave guide, meansfor propagating energy Within `said wave guide, a plurality of dif poles aligned along one of the walls of said Wave guide, means for shaping the radiation pattern produced by said dipoles, said means comprising two reflector plates one disposed above and the other below said aligned dipoles, said reflector plates `being arranged `at an angle to said wall of said wave guide and flared outwardly away from each other. one of said reflector plates having at least one bend along the length of the end portion remote from said wall, said bend being parallel to said wall and forming a secondary reflecting surface whereby an asymmetrical radiation pattern is obtained.

ROGER E. CLAPP.

REFERENCES CITED following references lare of record in the ille of this patent:

UNITED STATES PATENTS Humber Name Date 974,374 Gaggs Nov. 1, 1910 1,788,910 Buttolph Jan. 13, 1931 2,155,821 Goldsmith Apr. 25, 1939 2,198,903 Carter Apr. 3U, 1940 2,275,646 Peterson vMar l0, 1942 FOREIGN PATENTS Number Country Date 723,352 France Apr. 7, 1940 

